A combination of exhilaration and exasperation accompanies my reading of most Golden-Age (that is, 1937-1949) American superhero comic books. One can see both a genre and a medium being defined and refined, sometimes boldly, sometimes wrongly, sometimes ineptly. And as per Sturgeon's Law, at least 90% of it is crap. Maybe 99%.
Before the Avengers, the Justice League of America, the League of Extraordinary Gentlemen, the X-Men -- before all other superhero teams and superhero groups -- was the Justice Society of America, debuting in 1940 in issue 3 of All-Star Comics, just less than 3 years after the appearance of the first American superheroes. The group comprised the company now known as DC's Golden Age superhero stable, with a few notable exceptions: Superman and Batman were honorary members who almost never appeared, as the Society was used to help promote 'DC's' less popular heroes, while Wonder Woman would generally only act as recording secretary and not an actual fighting member of the group.
The most active original members of the JSA would range from the fairly famous (the original Green Lantern and original Flash) to the more obscure (comic relief Johnny Thunder and Red Tornado, the original Atom, Hourman, Dr. Fate, and the Spectre). Heroes with earth-shaking cosmic powers (the Lantern and his magic ring, Flash, Fate, Spectre and, surprisingly perhaps, Johnny Thunder and his magical intelligent pink thunderbolt) sat beside heroes with limited powers (Hourman, whose Miraclo pills gave him an hour of enhanced strength), powerful gadgets (Starman, Dr. Midnite, Hawkman, Sandman) or no powers or gadgets at all (the dreary Atom, whose power was that he was really strong for a height-challenged person. And he wasn't a really strong dwarf or midget -- he was maybe 5'2". Really, every JSA adventure should have ended with the dead body of the Atom being taken to Paradise Island to be revived with the super-healing Purple Ray, his revival being accompanied by the other heroes standing around laughing about how he got killed in every adventure by someone with a handgun or just a pointy stick. It wasn't until the Silver Age that a character named Atom got appropriate, and appropriately awesome, super-shrinking powers).
The first two issues of All-Star Comics published individual adventures of what would soon be Justice Society members; the third issue featured the origin of the Justice Society. And what an origin! A bunch of superheroes decide to get together in a hotel banquet room and talk during dinner!
OK, dramatic it's not. In the 1970's, writer Paul Levitz and artists Joe Staton and Bob Layton would give the JSA a truly awesome origin story, complete with Batman and Superman, but for now they are a jovial, joking sausage party (Wonder Woman was still a year away). They don't even fight crime together in that first issue, instead telling tales of individual heroism. But by issue 4, they were fighting crime in what would be the first model of a JSA story, individually tackling criminals in stories drawn by different artists (but all written by Gardner F. Fox) before coming together at the end of the story. Eventually, they'd do more teaming up, at least in pairs or trios, prior to the final gathering.
The art ranges from awful through competent to interesting. Sheldon Moldoff, later a Batman artist with a much different style, here does his best Alex Raymond impersonation on Hawkman; Bernard Baily does some really peculiar work on the Spectre; Howard Sherman does his typically weird, offbeat stuff (including the oddest lettering of the Golden Age) on Dr. Fate. The only real greatness here is the core concept of heroes getting together. As one can see from the hype surrounding next year's Avengers movie, that's still a concept with a lot of pop-cultural heft.